Baseline sodium-lithium countertransport and 6-year incidence of hypertension. The Gubbio Population Study

The Less Well-Known Little Brothers: The SLC9B/NHA Sodium Proton Exchanger Subfamily—Structure, Function, Regulation and Potential Drug-Target Approaches

The SLC9 gene family encodes Na+/H+ exchangers (NHEs), a group of membrane transport proteins critically involved in the regulation of cytoplasmic and organellar pH, cell volume, as well as systemic acid-base and volume homeostasis. NHEs of the SLC9A subfamily (NHE 1–9) are well-known for their roles in human physiology and disease. Much less is known about the two members of the SLC9B subfamily, NHA1 and NHA2, which share higher similarity to prokaryotic NHEs than the SLC9A paralogs. NHA2 (also known as SLC9B2) is ubiquitously expressed and has recently been shown to participate in renal blood pressure and electrolyte regulation, insulin secretion and systemic glucose homeostasis. In addition, NHA2 has been proposed to contribute to the pathogenesis of polycystic kidney disease, the most common inherited kidney disease in humans. NHA1 (also known as SLC9B1) is mainly expressed in testis and is important for sperm motility and thus male fertility, but has not been associated with human disease thus far. In this review, we present a summary of the structure, function and regulation of expression of the SLC9B subfamily members, focusing primarily on the better-studied SLC9B paralog, NHA2. Furthermore, we will review the potential of the SLC9B subfamily as drug targets.

A report on the Gubbio Study thirty-eight years after its inception

BACKGROUND

The Gubbio Population Study ("Gubbio Study") is a prospective epidemiological study carried out on the resident population of the city of Gubbio, Italy. The study's objectives are both of public health nature (the control and awareness of hypertension), and experimental (the role of electrolyte handling at the cellular membrane level and its relation to hypertension). Additional objectives were addressed during the 30+ year activity of the study, in particular the role of kidney dysfunction.

METHODS

Three active screenings ('Exams') were performed beginning 38 years ago; the first (Exam 1) in 1983-1986 (5376 individuals - response rate 92%) and two follow-up exams, were completed between 1989-92 (Exam 2) and 2001-2007 (Exam 3). Data collected include demographics, personal and family medical history, lifestyle (smoking, alcohol, diet and physical activity), education, type of work, anthropometry, blood pressure, pulse rate, blood biochemistry, urine biochemistry and special investigations on cellular electrolyte handling. Additional measurements were performed in selected sub-groups of participants. Data on hospitalizations, mortality and causes of death were collected after the completion of Exam 1.

RESULTS

The main results of the study, presented in this paper, identify new variables to consider in screening for cardiovascular risk factors, and show the impact that the focused and coordinated effort of a longitudinal program can have on a free-living population'.

CONCLUSIONS

The data are of relevance to Public Health and to experimental medicine alike, and vouch to the importance of the control of risk factors at the community level.

The sodium/proton exchanger NHA2 regulates blood pressure through a WNK4-NCC dependent pathway in the kidney

NHA2 is a sodium/proton exchanger associated with arterial hypertension in humans, but the role of NHA2 in kidney function and blood pressure homeostasis is currently unknown. Here we show that NHA2 localizes almost exclusively to distal convoluted tubules in the kidney. NHA2 knock-out mice displayed reduced blood pressure, normocalcemic hypocalciuria and an attenuated response to the thiazide diuretic hydrochlorothiazide. Phosphorylation of the thiazide-sensitive sodium/chloride cotransporter NCC and its upstream activating kinase Ste20/SPS1-related proline/alanine rich kinase (SPAK), as well as the abundance of with no lysine kinase 4 (WNK4), were significantly reduced in the kidneys of NHA2 knock-out mice. In vitro experiments recapitulated these findings and revealed increased WNK4 ubiquitylation and enhanced proteasomal WNK4 degradation upon loss of NHA2. The effect of NHA2 on WNK4 stability was dependent from the ubiquitylation pathway protein Kelch-like 3 (KLHL3). More specifically, loss of NHA2 selectively attenuated KLHL3 phosphorylation and blunted protein kinase A- and protein kinase C-mediated decrease of WNK4 degradation. Phenotype analysis of NHA2/NCC double knock-out mice supported the notion that NHA2 affects blood pressure homeostasis by a kidney-specific and NCC-dependent mechanism. Thus, our data show that NHA2 as a critical component of the WNK4-NCC pathway and is a novel regulator of blood pressure homeostasis in the kidney.

Osmotic indices and kidney concentrating activity: population-based data on correlates and prognostic power

Background

Research data are limited on indices of osmotic equilibrium and of kidney concentrating activity (KCA). This study investigated correlates and prognostic power of these indices in a sample of the general population.

Methods

Urine osmolality (U-osm), plasma osmolality (P-osm), plasma creatinine and other variables were measured by the Gubbio Study for the 1988-92 exam (baseline). Plasma creatinine and other variables were re-measured in the 2001-07 exam (follow-up). KCA was assessed as the U-osm/P-osm ratio and kidney function as estimated glomerular filtration rate (eGFR).

Results

Baseline data were complete in 4220 adults, of whom 852 died before follow-up and 2795 participated in the follow-up. At baseline, the following independent cross-sectional associations were identified: female sex and higher urine flow with lower values of U-osm, P-osm and U-osm/P-osm ratio (P < 0.01); obesity with higher values of U-osm, P-osm and U-osm/P-osm ratio (P < 0.01); older age and lower eGFR with lower U-osm, lower U-osm/P-osm ratio and higher P-osm (P < 0.05); hypertension and smoking with lower U-osm and lower U-osm/P-osm ratio (P < 0.05) but not with P-osm. From baseline to follow-up, the annualized rate was 1.26% for mortality and -0.74 ± 0.76 mL/min × 1.73 m2 for eGFR change. Mortality was independently predicted by baseline U-osm and baseline U-osm/P-osm ratio (hazard ratio for one higher standard deviation was ≤0.91, 95% confidence interval was ≤0.97, P < 0.01), but not by baseline P-osm. The eGFR change was not independently predicted by baseline values of U-osm, P-osm and U-osm/P-osm ratio (P ≥ 0.4).

Conclusions

Sex, age, obesity, eGFR, urine flow, hypertension and smoking independently associated with U-osm and KCA. U-osm and KCA independently predicted mortality, but not kidney function change over time.

Low Protein Intake in the Population: Low Risk of Kidney Function Decline but High Risk of Mortality

OBJECTIVE

This population-based study investigated low protein intake, mortality, and kidney function decline.

DESIGN

Observational longitudinal cohort study.

SUBJECTS

Target cohort consisted of 4,679 adults participating in 1988-1992 and 2001-2007 examinations of the Gubbio Study (baseline and follow-up). Data collection included overnight urine urea nitrogen (UUN) and other variables at baseline, serum creatinine at baseline and follow-up, and mortality from baseline to follow-up. Three hundred seventy-two persons were excluded for missing data. UUN in the lowest 20% of the distribution was defined as low and used as index of low protein intake. Estimated glomerular filtration rate (eGFR, mL/minute × 1.73 m²) was used as kidney function index.

INTERVENTION

None (observational study).

MAIN OUTCOME MEASURE

Mortality and eGFR decline are the main outcome measures, and eGFR decline was defined as eGFR change from baseline to follow-up ≤ mean-1 standard deviation (Z-score ≤ -1).

RESULTS

Eight hundred seventy-one deaths occurred over 15.9 ± 4.0 years of observation (417 from cardiovascular disease and 276 from neoplastic disease). Low UUN associated with mortality (hazard ratio, HR = 1.31, 95% confidence interval, CI = 1.12/1.53) due to association with mortality from neoplastic disease (HR = 1.33, 95% CI = 1.02/1.76). Mortality-corrected follow-up response rate was 79.9% (n = 2845). Baseline to follow-up eGFR change was -9.9 ± 10.1, and eGFR decline was found in 454 examinees. Low UUN associated with eGFR decline only in subgroup with baseline eGFR <90 (n = 1441, odds ratio = 0.44, 95% CI = 0.22/0.85). Low baseline eGFR interacted with the association between low UUN and eGFR decline (P = .024).

CONCLUSION

Low protein intake predicted higher mortality in the whole population and lower incidence of eGFR decline only in subgroup with reduced kidney function.

Cohort profile: The Gubbio Population Study

The Gubbio Study is a prospective epidemiological study on the population residing in the city of Gubbio, Italy. Original objectives of the study were the control of hypertension and the role of cellular electrolyte handling in hypertension. Other objectives were added during the 30-year activity of the study. The original target cohort consists of individuals aged ≥5 years residing within the medieval walls of the city. To complete family genealogies, individuals residing outside the city were also included. Three active screenings (exams) were conducted. A total of 5376 individuals (response rate 92%) participated in Exam 1 which was performed in 1983-86. Follow-up exams were completed between 1989-92 and 2001-2007. Data categories included demographics, personal and family medical history, lifestyle habits, education, type of work, anthropometry, blood pressure, pulse rate, blood biochemistry, urine biochemistry and special investigations on cellular electrolyte handling. Electrocardiogram, echocardiogram, 24-h ambulatory blood pressure and uroflowmetry were performed in selected subgroups defined by age and/or sex. Data about hospitalizations, mortality and causes of death were collected starting from completion of Exam 1. The study shared the data with other studies.

The role of HDL cholesterol in metabolic syndrome predicting cardiovascular events. The Gubbio population study

BACKGROUND AND AIMS

Metabolic syndrome (MS) has recently been claimed to be an important new risk factor for the occurrence of coronary heart disease (CHD) and cardiovascular disease (CVD) events, although it is simply a combination of known risk factors used in a dichotomized fashion. The aims of this analysis were to explore the predictive role of MS for CHD and CVD events in a population study, in comparison with using the same factors in a continuous fashion, with special emphasis on HDL cholesterol.

METHODS AND RESULTS

In the second examination of the Gubbio population study from central Italy, 2650 cardiovascular disease-free men and women, aged 35-74 years around 1990, were examined and followed-up for 12 years. The classic risk factors (sex, age, systolic blood pressure, serum cholesterol and smoking habits) were studied as predictors of CHD and CVD events, alone and with the contribution of other factors (HDL cholesterol, blood glucose, serum triglycerides and waist circumference) included in the so-called MS, based on several multivariate models. MS was also tested after adjustment for other risk factors. MS produced a predictive significant relative risk of 1.67 for CHD events and 1.82 for CVD events, but considering its single risk factors, the only ones contributing to prediction were HDL cholesterol and systolic blood pressure. Dedicated analyses showed that MS does not add anything to the power of prediction beyond the role of the single risk factors treated in a continuous fashion, while the best predictive power is obtained using classic risk factors (sex, age, smoking habits, total cholesterol, systolic blood pressure) with the addition of HDL cholesterol.

CONCLUSIONS

The predictive power of MS is bound only to the presence of HDL cholesterol and blood pressure and does not add anything to using the same risk factor treated in a continuous fashion.

Erythrocyte sodium-lithium countertransport activity is inversely correlated to adiponectin, retinol binding protein 4 and body height

BACKGROUND

We have previously described that the sodium/lithium countertransport (SLC) in the erythrocyte cell membrane is closely linked to obesity and insulin resistance. Adiponectin and retinol-binding protein 4 (RBP-4) are believed to affect obesity and insulin resistance. In the present study, we aimed to further characterize the relationship between SLC, inflammatory markers, adiponectin and RBP-4.

METHODS

We included 93 clinically healthy 58-year-old men selected to display variations in insulin sensitivity. High sensitivity C-reactive protein (hs-CRP), TNF-alpha, soluble TNF-alpha-receptors (sTNFR) 1 and 2, IL-6 and RBP-4 were measured using antibody-based techniques. Adiponectin was determined by a radioimmunoassay kit. The lithium concentration in the special flux medium was measured by atomic absorption spectrophotometry.

RESULTS

In univariate analyses, SLC correlated negatively with RBP-4 (r(s) = -0.256, p = -0.017) and to adiponectin (r(s) = -0.316, p = 0.003) and positively with TNF-alpha (r(s) = 0.346, p = 0.001) and hs-CRP (r(s) = 0.288, p = 0.005). There were no statistically significant correlations with sTNFR 1 or 2 or IL-6. SLC was negatively associated to body height (r(s) = -0.256, p = 0.013).

CONCLUSIONS

We are the first to report that SLC correlates negatively with adiponectin and RBP-4. This finding is intriguing, as adiponectin is anti-inflammatory and anti-diabetic whereas RBP-4 supposedly decreases insulin sensitivity. We also observed a negative association between SLC activity and body height indicating that SLC activity is not primarily influenced by fat mass. The positive association of SLC with markers of inflammatory activity such as TNF-alpha and hs-CRP is in line with the proposed link between inflammation and insulin resistance.

Glomerular filtration rate and serum phosphate: an inverse relationship diluted by age

BACKGROUND

Available data indicate that serum phosphate increases only when glomerular filtration rate (GFR) falls into the low range (<60 mL/min x 1.73 m(2)). GFR and serum phosphate decrease with ageing. This population-based study investigated by age-controlled analyses the relationship of GFR with serum phosphate in adults with GFR above the low range.

METHODS

Data were collected on age, sex, menstrual status, anthropometry, overnight urinary creatinine, dietary protein (overnight urinary urea), reported intake of milk/yogurt, serum creatinine, phosphate, calcium and total protein in 4034 adults (age 18-91 years) with GFR >or=60 mL/min x 1.73 m(2) as assessed by estimated GFR (eGFR, simplified MDRD equation) and creatinine clearance (overnight urinary creatinine/serum creatinine).

RESULTS

The relationship of eGFR with serum phosphate was positive in men and null in women in univariate analyses (P = 0.001 and 0.148), negative in both sexes with age adjustment (P < 0.001). Age-adjusted results did not depend on colinearity between age and eGFR because the relationship was inverse also replacing eGFR with creatinine clearance (P < 0.001 in both sexes). In univariate regression analysis done separately by gender and six age-strata (18-24, 25-34, 35-44, 45-54, 55-64 and >or=65), the line of serum phosphate over eGFR was constantly inverse (range of P = 0.010/0.089) with the progressively lower y-axis intercept from young to older ages. The inverse relationship of eGFR or creatinine clearance with serum phosphate was significantly inverse also controlling for other variables (P < 0.01).

CONCLUSIONS

GFR differences in the range >or=60 mL/min x 1.73 m(2) are inversely and independently related to serum phosphate. The relationship is undetectable without age-controlled procedures because, for serum phosphate, the effect of GFR differences above >or=60 mL/min x 1.73 m(2) is much smaller than the effect of age.

Low glomerular filtration in the population: Prevalence, associated disorders, and awareness

Estimated glomerular filtration rate (eGFR) was used for analysis of kidney disease prevalence in the United States. The study investigated on prevalence, associated disorders, and kidney disease awareness in an Italian population sample. Data were collected on serum creatinine, other laboratory indices, blood pressure, and medical history in the Gubbio Population Study (n=4574, both sexes, ages 18-95 years). Analyses were carried out on eGFR (equation of Modification Diet in Renal Disease study), disorders potentially secondary to kidney dysfunction (hypertension, high serum uric acid, high serum phosphorus/low serum calcium, high serum potassium, cardiovascular disease, anemia), and kidney disease awareness. The prevalence of eGFR <60 ml/min x 1.73 m(2) increased with age in both sexes (from <1% for ages 18-24 years to >30% for ages > or =75 years, P<0.001). In the group with eGFR <60 ml/min x 1.73 m(2), number of disorders secondary to kidney dysfunction was > or =2 in the majority of persons, was higher than in persons with eGFR > or =60 ml/min x 1.73 m(2) (P<0.001), and was inversely related to eGFR (P<0.001). The prevalence of reported kidney disease was 3.3% in the group with eGFR <60 ml/min x 1.73 m(2) and directly related to serum creatinine and number of disorders secondary to kidney dysfunction (P<0.001). Low kidney function is frequent in the older population and is associated with disorders typical of kidney disease. Persons with low kidney function are rarely aware of kidney disease unless of very high serum creatinine or presence of many disorders typical of kidney disease.

Urinary Albumin and Cardiovascular Profile in the Middle-Aged Population

The moderate increase in urinary albumin excretion defined as microalbuminuria is not rare and is associated with cardiovascular risk factors. Microalbuminuria prevalence is low in the absence of cardiovascular risk factors and progressively increases with the number cardiovascular risk factors. The main correlate of microalbuminuria is blood pressure, either systolic or diastolic pressure. The relation between blood pressure and microalbuminuria is continuous and graded because the microalbuminuria prevalence increases with the severity of hypertension. Among hypertensive patients on drug treatment, blood pressure control is associated with a low prevalence of microalbuminuria. Thus, blood pressure appears as a determinant of microalbuminuria rather than a mere correlate. For hypercholesterolemia, smoking, and diabetes, data are less strong but point to an independent positive association with microalbuminuria. Altogether, data indicate that microalbuminuria in the population reflects the presence of cardiovascular risk factors. Data on microalbuminuria and coronary heart disease support this idea. There is a continuous and graded relation between urinary albumin excretion and coronary heart disease prevalence. High urinary albumin excretion is likely a sign of vascular damage existing both at the renal and cardiac levels and induced by 1 or more uncontrolled cardiovascular risk factors.

Enhanced Na–Li countertransport: a marker of inherited susceptibility to type 2 diabetes

Introduction The association between type 2 diabetes and hypertension has long been described, but the mechanisms remain unclear. Na-Li countertransport (Na-Li CT) activity is viewed as a marker of inherited pre-disposition to hypertension, especially if associated with other metabolic abnormalities. Aim To evaluate whether enhanced Na-Li CT activity is a predictor of type 2 diabetes.

METHODS

Study participants were 2167 men and women, 30-70 years. Na-Li CT activity, glucose, HDL cholesterol, blood pressure, height, and weight were measured. Six years incidence of diabetes (WHO) was assessed.

RESULTS

Baseline Na-Li CT activity was significantly higher for people who developed diabetes at follow-up (n = 101) than for those who remained non-diabetic (364 +/- 184 vs 300 +/- 150 micromol/l RBC/h, P < 0.001). This finding was confirmed after correction for obesity, hypertension, and blood glucose. Six years' incidence of diabetes increased across tertiles of baseline Na-Li CT activity--from 2 to 7%--with a significant linear trend (P < 0.001). In multivariate analyses Na-Li CT is a significant predictor of diabetes independent of age, BMI, HDL cholesterol, hypertension, and plasma glucose; based on exponentiation of the regression coefficient Na-Li CT higher by 154 micromol (i.e. 1 SD of the population mean) was associated with a 36% greater risk of incident diabetes.

CONCLUSIONS

Prospective data from the present study show for the first time enhanced Na-Li CT activity is a significant predictor of development of diabetes in adults, thus suggesting that it could be viewed as a pre-clinical, possibly genetic, marker of inherited susceptibility to type 2 diabetes.

Baseline Na–Li countertransport and risk of hypertension in children: a 10-year prospective study in Hanzhong children

Sodium-lithium countertransport (Na-Li CT) is associated with blood pressure (BP) and in many cross-sectional investigations and some longitudinal studies, essential hypertension has been proposed as a biochemical marker or predictor of hypertension risk in adults. The present study investigated prospectively whether baseline Na-Li CT rate was an index of increased risk of future development of hypertension in children. At baseline visit in 1987 of the Hanzhong Children Hypertension Study comprising 4000 school children aged 5-6 years old, 310 samples were randomly selected for measurement of baseline Na-Li CT rate; we made a 10-year follow-up of them in the same season in 1997. This cohort of children is the sample for analysis in the present report. Baseline Na-Li CT rate was positively correlated to systolic BP (SBP) both in baseline and follow-up (baseline, gamma=0.21, P<0.05; follow-up, gamma=0.32, P<0.01), and positively correlated to diastolic BP (DBP) (gamma=0.20, P<0.05) and body mass index (gamma=0.18, P<0.05) in follow-up examination. Longitudinal analysis of 10-year BP evolution, children in higher baseline Na-Li CT (ie, >260 micromoll RBC/h) had greater BP change than children in lower baseline Na-Li CT (ie, </=260 mumol/l RBC/h) (SBP, 15.8+/-12.9 vs 19.3+/-13.1, DBP 8.8+/-11.2 and 11.3+/-10.6, P<0.05). Multiple logistic regression analysis showed that children in the higher Na-Li CT (>260 mumol/l RBC/h) were associated with approximately 1.5 times greater risk of high BP) in comparison to placement in lower Na-Li CT (</=260 mumol/l RBC/h). Elevated baeline RBC Na-Li countertransport could be a risk predictor predisposing to the development of hypertension in children.

Relation of urinary albumin excretion to coronary heart disease and low renal function: Role of blood pressure

BACKGROUND

Previous studies report that urinary albumin excretion is associated with coronary heart disease (CHD). The present epidemiologic study investigated if (1) blood pressure status affects the association of urinary albumin excretion with CHD; and (2) urinary albumin excretion is associated with low renal function also.

METHODS

The cross-sectional association was analyzed of overnight urinary albumin excretion with prevalence of CHD (myocardial infarction and/or ischemia as defined by standard electrocardiogram) and low renal function (overnight creatinine clearance <60 mL/min) in a population sample of 1632 men and women with ages 45 to 64 years. Hypertension, hypercholesterolemia, smoking habit, and diabetes mellitus were included in analyses.

RESULTS

CHD prevalence was in the whole sample 8.2% (N= 134), in the hypertensive subgroup 11.9% (N= 79), and in the nonhypertensive subgroup 5.7% (N= 55). For the association between urinary albumin excretion (logarithm-transformed due to skewed distribution) and CHD, the multivariate logistic coefficient with 95% CI was significant in the whole sample (+0.79, 95% CI =+0.32/+1.26, P < 0.001) and in the hypertensive subgroup (+0.97, 95% CI =+0.70/+1.24, P < 0.001), not in the nonhypertensive subgroup (-0.06, 95% CI =-0.80/+0.68, P= 0.997). Prevalence of low creatinine clearance was in the whole sample 4.0% (N= 66), in the hypertensive subgroup 4.8% (N= 32), and in the nonhypertensive subgroup 3.5% (N= 34). The logistic coefficient between urinary albumin excretion and low creatinine clearance was borderline significant in the whole sample (+0.56, 95% CI =-0.02/+1.14, P= 0.090), significant in the hypertensive subgroup (+0.73, 95% CI =+0.04/+1.42, P= 0.044), not significant in the nonhypertensive subgroup (-0.07, 95% CI =-1.25/+1.10, P= 0.913).

CONCLUSION

Results support the use of urinary albumin excretion as marker of CHD and slightly reduced renal function in hypertensives.

Effect of acute hyperglycemia on erythrocyte membrane ion transport in offspring of hypertensive parents

OBJECTIVE

Patients with essential hypertension exhibit several red blood cell (RBC) ion transport abnormalities, insulin resistance (IR) and increased risk of developing type 2 diabetes. The aims of this study were to assess RBC ion transport activities under basal conditions and to test the in vivo effect of acute hyperglycemia on RBC ion transport in the offspring of hypertensive parents (OHP) and healthy controls (C).

DESIGN AND METHODS

Activities of Na+-K+ pump, Na+-K+ cotransport, Na+-Li+ countertransport (SLC) and Na+, Rb+ and Li+ leaks were measured before and after a 5-h hyperglycemic (12 mmol/l) clamp (HGC) and compared to values found under euglycemic isovolumic conditions in OHP (n = 12) and C (n = 14). Insulin action was calculated as insulin sensitivity index (M/I) during HGC.

RESULTS

The offspring of hypertensive parents were characterized by lower M/I (0.07 +/- 0.03 versus 0.12 +/- 0.07 mg/kg per min per microU per ml; P < 0.05) and elevated SLC (0.080 +/- 0.004 versus 0.068 +/- 0.003 mmol/h per litre; P < 0.05), as well as by higher Li+ (0.106 +/- 0.004 versus 0.093 +/- 0.003 mmol/h per litre; P < 0.05) and Rb+ leaks (0.160 +/- 0.014 versus 0.120 +/- 0.007 mmol/h per litre; P < 0.05) compared to controls. Acute hyperglycemia did not cause significant changes in any investigated RBC ion transport parameters.

CONCLUSIONS

The offspring of hypertensive parents displayed higher insulin resistance, enhanced activity of SLC and formerly undocumented augmented Li+ and Rb+ leaks. Acute hyperglycemia did not modify any RBC ion transport activities in either offspring of hypertensive parents or controls.

Cross-sectional and prospective data on urinary calcium and urinary stone disease

BACKGROUND

Urinary calcium is considered a risk factor for urinary stone disease (USD), although prospective data are missing. This epidemiologic study investigates cross-sectionally and longitudinally the relation of urinary calcium excretion to USD.

METHODS

In the Gubbio Population Study, data on USD were collected by questionnaire during medical examinations from 1989 to 1992 (baseline) and telephone interviews in 1997 to 1998 (follow-up). Baseline data collection included overnight urinary calcium excretion and use of medications. Study cohort was made of 1458 men and 1799 women, age 25 to 74 years, and not on treatment with diuretics at baseline. USD was diagnosed by: excretion of stone(s), and/or radiographic or ultrasonic evidence, and/or surgical or endoscopic removal of stone(s).

RESULTS

At baseline, urinary calcium excretion was higher in persons with than without USD (215 and 182 micromol/hour, P < 0.001) and related to USD prevalence independent of gender, age, and other variables (P < 0.001). Among persons without USD at baseline, baseline urinary calcium excretion was higher in persons with than without incident USD at follow-up (202 and 181 micromol/hour, P = 0.034) and related to incident USD independent of gender, age, and other variables. A difference of 100 micromol/hour (about 1 SD) in urinary calcium excretion related to a difference in USD risk of 1.32 for prevalence and 1.21 for incidence (95% CI = 1.15/1.52 and 1.01/1.45, respectively) in multivariate analyses controlled for gender, age, body mass index, parental history of USD, urinary excretion of urea, sodium, and potassium.

CONCLUSION

Cross-sectional and prospective data show that urinary calcium excretion is a risk factor for USD.

Alternative splicing of NHE-1 mediates Na-Li countertransport and associates with activity rate

Sodium-lithium countertransport (SLC) is an ouabain-insensitive exchange of Na for Li found in the erythrocyte membrane of several mammalian species. Although increased SLC activity is presently the most consistent intermediate phenotype of essential hypertension and diabetic nephropathy in humans, the gene responsible for this membrane transport has not been identified. Because of functional similarities, SLC was suggested to represent an in vitro mode of operation of the Na-H exchanger (NHE). This hypothesis, however, has been long hampered by the total insensitivity of SLC to amiloride, which is an intrinsic inhibitor of the first isoform of NHE, the only NHE isoform detected in human erythrocytes. We describe here the identification in human reticulocytes and erythrocytes of an alternative splicing of NHE lacking the amiloride binding site. Transfection experiments with this spliced variant restore amiloride-insensitive, phloretin-sensitive SLC activity. Expression of both regular and spliced transcripts of NHE is increased in subjects with high SLC activity. Altogether, these findings, by extending to NHE the characteristics of inheritance and predictivity previously attributed to SLC, eventually restore the candidacy of NHE isoform 1 as a gene involved in the pathogenesis of essential hypertension and diabetic nephropathy.

Increased red cell sodium-lithium countertransport and lymphocyte cytosolic calcium are separate phenotypes in patients with essential hypertension

Increased red blood cell sodium-lithium countertransport (SLC) activity and elevated intracellular calcium have been observed in hypertensive patients. The association of these ion transport abnormalities with each other and with another phenotype, insulin resistance, has been suggested. We investigated whether elevated SLC activity and increased lymphocyte cytosolic calcium (Ca(cyt)) occur in the same individuals and whether either is associated with hyperinsulinaemia. We measured SLC activity, lymphocyte Ca(cyt)and fasting insulin levels in hypertensive patients and normal subjects. Consistent with prior studies, SLC activity was significantly and positively correlated with fasting insulin levels (r = 0.45, P < 0.01). However, SLC activity and lymphocyte Ca(cyt) were significantly but inversely correlated (r = -0.42, P < 0.01) and lymphocyte Ca(cyt) was also inversely correlated with fasting insulin (r = -0.55, P < 0.001). When the study participants were instead separated into two groups based on fasting insulin levels, those above the median (15 microU/ml) had significantly higher SLC activity and significantly lower Ca(cyt). When separated by lymphocyte Ca(cyt) levels (above or below 120 nM) those patients with low lymphocyte Ca(cyt) had significantly higher SLC activity and significantly higher insulin levels. Multiple linear regression showed that fasting insulin was significantly predictive of SLC activity (P = 0.05) and Ca(cyt) (P < 0.01). Thus, elevated SLC activity and increased lymphocyte Ca(cyt) are separate and distinct ion transport phenotypes in hypertensive patients, linked through a relationship to hyperinsulinaemia that is direct with SLC activity and inverse with lymphocyte Ca(cyt).

Relation of urinary urea to blood pressure: interaction with urinary sodium

A previous study reported that urinary markers of protein intake are inversely related to blood pressure via unknown mechanisms. In man and rats, protein intake affects renal function and increases renal sodium excretion. The present study investigates the relation between markers of protein intake and blood pressure and the possible role of sodium in this relation. Blood pressure status, overnight urinary urea as index of protein intake, urinary and plasma sodium, and other variables were measured in a population sample of 3705 men and women, aged 25-74 years, without high plasma creatinine. Urinary urea was inversely related to blood pressure and hypertension: in multivariate analyses, 6.5 mmol/h higher urinary urea (about one s.d. in men and women) was related to 4.25 mm Hg lower systolic blood pressure (95% confidence interval = 1.34-8.49), and to 0.65 lower risk of hypertension (95% CI 0.34-0.87). An interaction was found between overnight urinary sodium and the relation of urinary urea to blood pressure: the relation was significant only in persons with overnight urinary sodium above the median. Urinary urea was significantly and inversely also related to plasma sodium. Data confirm an inverse relation to blood pressure of protein intake as measured by urinary urea. The possibility of sodium-related mechanisms is supported by the interaction of urinary sodium with the relation and by the inverse association of urinary urea with plasma sodium. The hypothesis is made that high protein intake could counteract sodium-dependent blood pressure rise via stimulation of renal sodium excretion.

Fibroblast Na+-Li+ countertransport rate is elevated in essential hypertension

OBJECTIVES

Elevated erythrocyte Na+- Li+ countertransport (SLC) rates are commonly found in essential hypertension. We have recently shown that human skin fibroblasts functionally express a phloretin-sensitive Na+-H+ exchange (NHE) which may also be similar to erythrocyte SLC because of amiloride-insensitivity.

DESIGN AND METHODS

We investigated whether elevations in fibroblast SLC parallel the known elevations in erythrocyte SLC and in cell NHE that characterize essential hypertension.

RESULTS

Higher fibroblast SLC rates were found among hypertensive patients (n = 23, median 48.8 nmol Li+/ mg(protein) per min) than in 19 normotensive individuals of similar age and sex (median 14.8 nmol Li+/mg(protein) per min, P= 0.0002). As expected, erythrocyte SLC was elevated in patients with hypertension (median 411 versus 329 micromol/l(cell) per h, P= 0.0273), but was not quantitatively related to fibroblast SLC. Finally, fibroblast NHE exchange activity was higher in essential hypertension (median Vmax 14.2 versus 7.6 mmol H+/l(cell) per min, P= 0.002), but was unrelated to fibroblast SLC.

CONCLUSIONS

These findings extend to human skin fibroblasts the notion of abnormal Li+ transport in essential hypertension, and appear to be in accordance with the hypothesis that fibroblast SLC may be independent of NHE. However, molecular studies will be required to understand whether distinct exchangers and/or regulation mechanisms underlie these dysregulations.

Impact of the Gubbio population study on community control of blood pressure and hypertension. Gubbio Study Research Group

BACKGROUND

Awareness and treatment of hypertension have markedly increased in the last 30 years in most parts of the world, but a satisfactory control of blood pressure is still infrequent

OBJECTIVES

To describe trends in community control of hypertension and blood pressure levels in the small town of Gubbio, Italy.

METHODS

Large samples of the populations (aged 30-79 years) were examined 6 years apart for measurement of blood pressure, other cardiovascular risk factors and knowledge, attitude and practice towards control of hypertension. Data were available from a total of 1125 men and 1445 women with two examinations and 1566 men and 1658 women with at least one examination. Two different definitions of hypertension were used (old definition: systolic blood pressure (SBP) > or = 160 mmHg or diastolic blood pressure (DBP) > or = 95 mmHg or use of antihypertensive drugs; recent definition: SBP > or = 140 mmHg or DBP > or =90 mmHg or use of anti-hypertensive drugs).

RESULTS

Awareness, treatment and control of hypertension increased from one survey to the other, whatever definition of hypertension was used. Control rose from 41 to 63% (old definition) and from 12 to 24% (recent definition). In a 6-year period, the average population SBP declined 2-8 mmHg and DBP declined 2-3 mmHg depending on type of analysis, against an expected rise of 9 mmHg for SBP and 2 mmHg for DBP. These trends are partly explained by a marked decline in alcohol consumption and by more common and intensive anti-hypertensive treatment, while change in body mass index, which showed a slight but systematic increase, cannot be considered as a contributor to this trend.

CONCLUSIONS

An epidemiological study has motivated a population group and its medical profession towards a better control of hypertension.

Pulse pressure and isolated systolic hypertension: association with microalbuminuria. The GUBBIO Study Collaborative Research Group

BACKGROUND

The long-term risk of end-stage renal disease is high in persons with isolated systolic hypertension, that is, those with an elevation of pulse pressure and not of diastolic pressure. Other data suggest that pulse pressure is a predictor of the hypertension-induced organ damage. Microalbuminuria is considered an early sign of glomerular damage caused by hypertension. The study shows the relationship of pulse pressure and isolated systolic hypertension to microalbuminuria in nondiabetic subjects.

METHODS

This is a cross sectional analysis for a population sample of 677 men and 890 women, aged 45 to 64 years, who were without diabetes mellitus and macroalbuminuria. Data collection included: overnight urinary albumin and creatinine excretion; fasting plasma glucose, cholesterol, and creatinine; creatinine clearance; and blood pressure, weight, height, medical history, and smoking habit. Pulse pressure was calculated as systolic minus diastolic pressure. Isolated systolic hypertension was defined as systolic pressure > or =140 mm Hg in persons not on antihypertensive drugs and with diastolic pressure <90 mm Hg. Microalbuminuria was defined as urinary albumin excretion > or =20 microg/min.

RESULTS

Pulse pressure and isolated systolic hypertension were significantly related to urinary albumin excretion and the prevalence of microalbuminuria in univariate and multivariate analyses. Controlling for gender and other variables, the risk of microalbuminuria was 1.71 with a 15 mm Hg higher pulse pressure (95% CI, 1.31 to 2.22) and 4.95 in the presence of isolated systolic hypertension (95% CI, 3.15 to 7.76).

CONCLUSIONS

In nondiabetic, middle-aged adults, pulse pressure and isolated systolic hypertension are directly related to microalbuminuria, independent of diastolic pressure and other correlates.

Relevance of erythrocyte Na+/Li+ countertransport measurement in essential hypertension, hyperlipidaemia and diabetic nephropathy: a critical review

In this review the usefulness of the measurement of erythrocyte Na+/Li+ countertransport (Na+/Li+ CT) activity is evaluated. In particular, the association between enhanced erythrocyte Na+/Li+ CT activity and essential hypertension, hyperlipidaemia and diabetic nephropathy is discussed. The conclusion of this review is that elevated erythrocyte Na+/Li+ CT activity is associated with essential hypertension and hyperlipidaemia. A relationship between Na+/Li+ CT activity and diabetic nephropathy is less evident. Despite a significant link of Na+/Li+ CT activity with hypertension and hyperlipidaemia, the diagnostic significance of Na+/Li+ CT activity is low. This is due to the large overlap between the results of control subjects and patients. The factors that contribute to this broad range are discussed in detail.